The term ‘optical switch’, as used herein, refers generally to a device that reflects incident light, when the light is at a low level of intensity, transmits only a portion of the incident light at intermediate intensities, and saturates transmitted intensity for high incident intensities. The threshold for the partially transmitting behavior is half of that for saturation and is explicitly defined in terms of material parameters.
Currently, most of complex signal-processing operations such as switching, logic functions, or routing are done in the electrical domain. This necessitates costly electro-optical and opto-electrical conversions. Suitably deployed, all-optical devices could reduce or eliminate the need for repeated EO and OE conversion, simplifying optical networks.
A variety of non-electronic switches have been proposed. As discussed in detail in Salech & Teich, Fundamentals of Photonics, pp. 843-855 (1991), hereinafter Salech & Teich, most non-electronic switches are opto-mechanical, electro-optic, acousto-optics or magneto optics switches. All of these approaches require external switching, hence are not passive. In addition the time of response of such switches is limited by the driving mechanical, electrical, acoustic or magnetic control.
Fully optical devices usually rely on the principle of bistabiltiy as discussed in detail in Salech & Teich, pp. 843-855. A drawback of bistable devices is that, for some incident intensities, there may be two or more possible transmitted intensities. The instantaneous state of transmission or reflection may thus depend upon the history of the state of transmission and such devices may additionally exhibit chaotic behavior.